U.S. Pat. No. 4,643,801 discloses improved retention and drainage during paper making through the use of coacervate additive system of dispersed silica in combination with anionic and cationic polymers. An improvement in paper formation was also noted. The dispersed silica may take several forms but polysilicate microgels were not disclosed.
U.S. Pat. No. 5,126,014 discloses improved retention and drainage from the use of colloidal silica or bentonite in combination with at least two cationic polymers and an anionic polymer. This patent also explores the conflict and difficulty in achieving optimum formation on the one hand and optimum retention and drainage on the other in paper making. Everyday paper making requires choices depending on which property is more important at any particular time.
U.S. Pat. No. 4,954,220 discloses the utilization of polysilicate microgels in paper making in combination with cationic polymer to achieve improved retention and drainage. Similar process improvements are disclosed in U.S. Pat. No. 4,927,498 by the use of polyaluminosilicate microgel with cationic polymer. The formation (or evenness) of paper is a highly important property which affects many of the paper's overall properties, such as tensile and tear strength, the amount of expansion and contraction occurring at different moisture levels and its appearance and printability. Good formation is important on all grades of paper but particularly in light-weight freesheet for printing. Chemical additives are frequently added to the wet-end of a papermaking process to control formation and also other operating properties such as retention and drainage. In commercial practice, good paper formation must also be accompanied by good retention and drainage, since, if these latter are inadequate, a limit is placed on production. Production requirements force papermakers to focus on improving retention and drainage while maintaining formation within an acceptable range. Consequently, any additive system which might improve paper formation and, at the same time, maintains or increases retention and drainage properties would represent a significant advance.